1. Field of the Invention
The present invention relates to an electronic device for cycling rechargeable batteries and specifically to an electronic device for the automatic discharging and charging of nickel cadmium batteries.
2. Description of the Prior Art
Nickel cadmium batteries exhibit a phenomenon termed "memory" (subsequently described) when the batteries are repeatedly charged at a high rate after being only partially discharged. The development of the memory effect is accelerated when the depth of discharge is low and the rate of charge is high.
Memory in nickel cadmium batteries is the premature drop in the batteries' nominal discharge curve which seriously degrades the batteries' usefulness in terms of performance predictability and life. Memory can usually be removed from nickel cadmium batteries by repeated cycling of the batteries, i.e., discharging the batteries to the proper level and then recharging them at a slow rate. However, the memory effect can be avoided altogether by properly cycling the batteries on a regular basis from the beginning. This will greatly increase the batteries' life as well as enable them to perform predictably. The present invention provides a simple, low cost means for accomplishing nickel cadmium battery cycling.
Numerous devices exist which perform the discharging and charging of nickel cadmium batteries but these devices are complicated and require technical knowledge on the part of the consumer. The level of sophistication of these existing devices drives a high consumer cost which imparts reluctance onto the consumer to purchase the device. The present invention requires no technical knowledge to operate, is completely automatic, and is relatively inexpensive.
During the patent search, one particular issued patent bore some similarity to the present invention and is discussed in detail below.
Reference U.S. Pat. No. 4,517,517 to Kinney. The first major shortcoming of the reference patent is that the controlling circuitry is powered from the battery under test (block 10a). The operational amplifier, .mu.A 741, has a finite range of supply voltages required for proper operation. If the voltage of the battery under test falls below this finite range or exceeds this finite range, the operational amplifier will not function rendering the circuit inoperative. Furthermore, a specific voltage range must be maintained across the Zener diode Z1 in order to maintain it in reverse bias. Again, if the voltage of the battery under test falls below or rises above this specific range, the Zener diode will not function rendering the circuit inoperative. The present invention differs from the reference patent in this regard in that the controlling circuitry is powered by an autonomous power supply and not by the battery to be cycled.
Secondly, the reference patent does not provide a means for automatically entering the charge mode upon termination of the discharge cycle; this must be effected manually by an operator or user, which requires constant monitoring of the device while in operation. The present invention automatically enters the charging mode upon completion of the discharge cycle and requires no user intervention or monitoring whatsoever.
Thirdly, the reference patent does not provide a means for completely isolating the battery under test from the circuit upon completion of the discharge cycle; the battery under test remains loaded by the circuit. This continues to discharge the battery, however, at a slower rate, and, if left unattended, would eventually completely discharge the battery and possibly damage the battery permanently. Since the present invention automatically switches into the charge mode upon completion of the discharge mode, the possibility of complete battery discharge is eliminated.
The present invention is a great departure from the reference patent and the present invention is far superior to the reference patent with regard to any similarities between the two.